This invention relates to a method and apparatus for etching substrates having a coating selected from the group consisting of semiconductor coatings, metallic coatings, and mixtures thereof.
There are numerous articles which contain a relatively expensive base substrate which receive, or serve as the foundation for, subsequent coatings selected from the group consisting of semiconductor coatings, metallic coatings, and mixtures thereof. These articles are typically produced by successively building up coatings, layers of materials, and/or substrates on the base substrate, and/or materials which are subsequently built up from base substrate. The manufacture of these articles is made more costly by the relative frequent occurrence of defective deposition of conductive coatings.
One example of such an article is a cadmium telluride photovoltaic (CdTe PV) solar cell module. CdTe PV solar cell modules are typically made by providing a base substrate comprising a first glass layer having a coating of tin oxide (SnO2) deposited thereon, depositing a coating of semiconductor cadmium sulfide (CdS) over the tin oxide coating, then depositing a coating of semiconductor cadmium telluride (CdTe) over the cadmium sulfide coating, then adhering a metal contact layer onto the cadmium telluride coating, then adhering a layer of polymeric material, such as ethylene-vinyl acetate (EVA), onto the metal contact layer, followed by adhering a second glass layer onto the polymeric layer.
Each coating or layer is built up onto the underlying coating or layer in successive steps. After each coating is deposited, the coating is analyzed to ensure that the coating has been properly deposited. Any solar cell module formed with defective coatings would itself be defective. Processing errors in the deposition of the cadmium sulfide coating or the cadmium telluride coating occur with relative frequency, such as on the order of about 10% of the time. Examples of processing errors include, but are not limited to, improper coating thickness and insufficient coating uniformity.
As a practical matter, substrates which have been improperly coated are often discarded, rather than recycled, because there has not been an inexpensive, convenient, and easy method for removing the improperly deposited coatings while leaving the substrate intact. It would be desirable to provide an inexpensive method for removing improperly deposited conductive coatings without damaging the base substrate intact.
One object of the present invention is to provide an inexpensive method for removing coatings from substrates having a coating selected from the group consisting of semiconductor coatings, metallic coatings, and mixtures thereof while keeping the substrate intact.
Another object of the present invention is to provide an apparatus having a small footprint which is capable of removing coatings from substrates having a coating selected from the group consisting of semiconductor coatings, metallic coatings, and mixtures thereof while keeping the substrate intact.
Yet another object of the present invention is to provide an inexpensive method for removing defective cadmium coatings from cadmium telluride photovoltaic solar cell module subassemblies while leaving the glass substrate intact with the tin oxide coating adhered thereto.
Still yet another object of the present invention is to provide an apparatus having a relatively small footprint which is capable of removing defective cadmium coatings from cadmium telluride photovoltaic solar cell module subassemblies while leaving the glass substrate intact with the tin oxide coating adhered thereto.
In carrying out the above, and other, objects, the present invention provides a method for etching substrates having a coating selected from the group consisting of semiconductor coatings, metallic coatings, and mixtures thereof. The method comprises providing at least a first and a second substrate having a coating selected from the group consisting of semiconductor coatings, metallic coatings, and mixtures thereof and introducing at least the first substrate and an etchant into a first tank to etch at least a portion of the coating from the substrate. At least the second substrate is introduced into a second tank and the etchant is transferred from the first tank to the second tank to etch at least a portion of the coating from the second substrate. The etched first substrate is then removed from the first tank.
The present invention also provides an apparatus for etching substrates having a coating selected from the group consisting of semiconductor coatings, metallic coatings, and mixtures thereof. The apparatus comprises a first tank for receiving a substrate having a coating selected from the group consisting of semiconductor coatings, metallic coatings and mixtures thereof. The apparatus also includes a second tank for receiving an etchant, and a pump for pumping the etchant from the second tank to the first tank to etch at least a portion of the coating from the substrate and for thereafter pumping the etchant back to the first tank.
The present invention further provides a method for etching a substrate having a coating selected from the group consisting of semiconductor coatings, metallic coatings, and mixtures thereof. The method comprises introducing the substrate into a first tank. An etchant capable of etching the coating from the substrate is introduced into a second tank. The etchant is transferred from the second tank to the first tank to provide etching of at least a portion of the coating from the substrate within the first tank. The etchant is transferred from the first tank back to the second tank, and the etched substrate is then removed from the first tank.
The objects, features and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.